Mitchell served as U.S. Special Envoy for Middle East Peace from 2009 to 2011 and in the Senate from 1980 until 1995, including a tenure as Senate Majority Leader.

He argued both Israel and Hamas have made “immediate gains” either militarily or politically.

“Hamas is gaining politically,” he said, because Palestinian Authority President Mahmoud Abbas is “sidelined and increasingly losing political support.”

Mitchell said he’s optimistic about the prospects for a solution soon.

“I think that eventually it will happen, that it’s so much in the interest of both societies, that there be a resolution for this conflict,” he said.

Israel's Defense Forces, however, ramped up their operation on Monday inside the Gaza Strip to destroy Hamas-built tunnels that lead into israel. Prime Minister Benjamin Netanyahu told Israelis to prepare for a "prolonged" operation.

Mitchell’s comments backing Kerry comes the day after White House deputy national adviser Tony Blinken also defended Kerry against Israeli criticism, saying there is “no stronger defender” than Kerry for Israel and peace in the region.

Reports from Israeli media over the weekend said Israeli officials accused Kerry of “capitulating” to Hamas in cease-fire talks last week.

State Department spokeswoman Jen Psaki and Blinken pushed back against those allegations on Monday, explaining that the drafted cease-fire Israel rejected on Friday was not a U.S. proposal. They said it mirrored the original Egyptian-sponsored proposal from mid-July, which Israel had accepted and Hamas rejected.